Printing plate material



April 10, 1956 s. VAMVAKETIS 2,741,297

PRINTING PLATE MATERIAL Filed May 9, 1952 14 1/4444\x'rzza azz zzzINVENTOR.

J'Tf/ HE/V V4MV4/i f7/J' BYy hg/y AGENT United States Patent '9 PRINTINGPLATE MATERIAL Stephen Vamvaketis, Cranston, R. 1., assiguor to United:States Rubber Company, New York, N. Y., a corporafion of New JerseyApplication May 9, 1952, set-m No. 286,898

1 Claim. c1. 154-54 'This invention relates to an improved printingplate material, and more particularly it relates to -a printing platematerial that is adapted for convenient preparation of printing plateshaving improved characteristics.

The printing plate materials and the printing plates available inaccordance with prior art practices have had certain disadvantages.Thus, printing plates made from metals or rigid plastics have lacked theflexibility that would be desirable to permit easy mounting of theplates on the cylinders of the printing press. Also, the lack ofresiliency, in addition to the hard surface of these materials,sometimes led to cutting or undesirable embossing of delicate surfaces,such as cellophane, glassine, tissue paper, etc., on which it wasdesired to print. Furthermore, the handling and storing of the metalorrigidplastic plates required extreme care, since such plates wereeasily damaged by contact with other hard objects, or when dropped onthe floor.

On the other hand, printing plates made from resilient materials do notlend themselves to the reproduction of fine details, as is required inmost letterpress work, 'because of their tendency to deform and spreadout under normal printing pressure.

The present invention has for its principal object the amelioration ofthe foregoing difiiculties by provisionof a printing plate materialwhich is easily fabricated into a printing plate that has a printingsurface capable of accurately reproducing fine detail, but that at thesame time is flexible and resilient Another object is the provision of aprinting plate material which is easily manufactured and can be shippedconveniently in bulk, and stored for relatively long periods withoutdeterioration.

Still a further object of the invention is to provide a printing platematerial which the ordinary rubber or plastic printing plate maker canutilize conveniently and efiiciently, in its present plate makingequipment.

Additional objects and advantages of the invention will be made manifestin the following detailed description, which isintended to be read withreference to the accompanying drawing, wherein:

Fig. l is a transverse sectional view of a sheet of printing platematerial made in accordance with the invention;

Fig. 2 is a similar view on a smaller scale of the material rolled upfor shipment or storage;

Fig. 3 .is a view similar to Fig. 1 showing the sheet after fabricationinto a printing plate; and,

Fig. 4 is a similar view of the printing plate applied to the cylinderof a printing press.

The invention provides a printing plate material in the form of alaminated sheet constituted essentially of a relatively thick resilientbacking sheet of soft rubber in the unvulcanized state, having adheredto one surface a tat-ea en na- 12 '2 relatively thinner layer of a hardbut flexible blend of a thermosetting resin with a synthetic rubber. Thesaid thermosetting resin is most preferably a phenolic resin and thesaid synthetic rubber is most preferably of the type known as nitrilerubber (also known as Buna N, or by such trade names asHycar-or-Paracril).

Referring to the drawing, and in particular toFig. 1, there is shown asheet of such laminated printing plate material having a softvulcauizable rubber backingl l, and a facing 2 composed of 'a hardphenolic resin-nitrile rubber blend. The rubber backing 1 is preferablyalso made of nitrile rubber for best resistance to the solvents or oilslikely to be encountered in printing practice. The soft backing istypically made about 0:03 to 0.4 inch thick, and the hard facing isusually about 0.005 to 0.05 inch thick. The backing is generally madefrom 3 to 10 times thicker than the facing.

The backing is so compounded, in a manner that will be understood'bythose skilled in the art of rubber compounding, as to be vulcanizable,at the usual molding temperatures, to a soft vulcanized state, such thatthe vulcanized material has a Shore hardness within the range from 15 toon the Shore A scale. When using the accelerators and activatorscommonly used :for sulfur vulcanization of nitrile rubber, in theamounts customarily employed, it will generally be found that thebacking composition will have the proper hardness when compounded withfrom 0.5 to 5.0 parts of sulfur, although the skilled rubber compounderwill be able to ,produce the desired hardness with amounts of sulfuroutside of wthisrange.

In formulating the tough facing composition, there is employed asoluble, heat-reactive phenolic resin, prepared from phenol andformaldehyde 'byacid catalysis, suchas is described, for example, in U.S. Patent 2,203,206 of Shepard et al. The phenolic resin preferably ismodified with from 2 to 10% of cashew nut oil. Such resins are mutuallycompatible with, or soluble in, the nitrile rubber component, and theyare c'apable of being converted into a relatively infusible, insolublestate by'heating in the presence of a curing agent, which is usually asubstance capable of yielding formaldehyde, as is well understood bythose skilled in the art. With'from 20 to 150 parts by weight of suchphenolic resin, there is admixed parts of the nitrile rubber to'make'thetQughfacing'compound. Thenitrile rubber may be any suitable rubberybutadiene-acryl'onitrile copolymer of commerce containing from 10 to 50%of'conibined acrylonit'rile by weight, and more preferably containingabout 20-to 45 of acrylonitrile. The phenolic resin andthe "nitrilerubber may be blended together by any suitable procedure, such as'bymixing together on-a rubbermill.

The facing formulation should include an agent capable of promoting theheat-setting of the phenolic resin, such as hexamethylenete'tramine inamount of from '4 to 12 parts per 100 parts by weight of resin.'Frequentlythe commercial grades of phenolic resin already contain'a'curing'agent. I

i "It is also advantageous to include a small amount of sulfur in "the-mixture,-say l 'to "10 parts per 100 parts 'of rubber, particularly ifthe mixture contains less than about '50 parts of phenolic resin 'in 100parts of nitrile rubber. i i

Phenolic resin nitril'e rubber blends of this type produce, upon'curingat elevated temperatures'ya composition which'is unusually'hardand tough, but still definitely flexible, "and having physicalproperties which are un- "usually well suited for printing. The curedmaterial has a Shore hardness within the range from 65 to 100 ontheunfilled, or it may be filled with various materials, such as carbonblack.

The following example will illustrate the invention in further detail.

A commercial nitrile rubber sold under the trade designation ParaerilBJ.

Face compound Paracril Bl 100.00 Phenolic resin 70.00 Zinc oxide 1 5.00Carbon black 100.00 Stearic acid 0.75 Cumarone-indene resin 25.00Antioxidant 0.75 Accelerator 2.00 Sulfur 5.00

A novolac type of cashew nut shell oil modified phenolic resincontaining hexamethylenetetramine as a curing agent, sold under thetrade designation Durez 12687.

A viscous liquid type of resin, sold under the trade designation CumarAX.

The compounds were mixed on a roll mill and lamination of the twocompounds was affected on a calender.

The heat and pressure of the calender-lug operation cause .7

the two layers to become firmly united. The adherence of the two layersis enhanced by the fact that the nitrile rubber constituting the backinglayer is also present in the facing layer. 7 r

The resulting laminate was 0.125 inch thick, comprising 0.02 inch offacing and 0.105 inch of backing. The laminate was flexible and couldeasily be rolled up into a roll 3 as shown in Fig. 2, for storage orshipping. To prepare'a printing plate from this laminate, a piece of thematerial was simply cut from the roll 3 to the size of the matrix, whichinthis case was made of Bakelite and was previously'prepared by sprayingwith a silicone mold release emulsion composition, followed by dustingwith fine talc. The piece of laminate was placed on top of the matrixand the assembly wasthen placed between 'the platens of a vulcanizingpress between thickness bearers to control the thickness of the finishedplate. I The press was closed to effect a preliminary dwell, duringwhich the material of the plate was pre-heated by contact with theplatens, but without being actually compressed. After one minute of suchdwell, a platen pressure of about 125 pounds per square inch was appliedfor about 8 minutes at 307 F. during which time both the backing and theface material became completely cured. The

cured plate, havingthe appearance shown in Fig. 3, with the printingimpressions 4 molded in its face,-was removedfrom the matrix, the flashwas trimmed off, and

of the plate, although hard and smooth, was not brittle.

It was found by actual use of such a plate, that the surface was rigidenough to print fine detail. The flexible and resilient rubber backingabsorbed practically all of the printing pressure, and at the same timecompensated for any irregularities in the printing surface, as well asany unequal printing pressure. Because the plate could be mounted on thepress substantially as easily as a rubber plate, the presentconstruction, permitted costly make ready time" to be minimized.

Because the printing plate material made in accordance with theinvention takes the form of a sheet material, the storage, shipment andutilization of the material is greatly simplified. Since the surface ofthe material isrnot easily damaged, the usual hazards in storing andshipping the plate or the material are substantially eliminated.

The printing plate maker can utilize the material conveniently andefiiciently, since the material is fabricated to the prescribedthickness, and the plate maker can simply convenient than the useofresins and the like in granular form. In molding a plate from thelatter materials, it was necessary to first spread the granules over thematn'x,'and then wipe out the excess so that the granulesremained onlyin the crevices of the matrix. Since many matrix designs are intricate,the process of distributing the granules evenly was time consuming, andproved to be very diflicult in 'many cases. V Y

The plates made from the present material are not only capable ofprinting fine detail with accuracy, but they are unusually long wearing,and retain their ability to print fine detail even after prolongedperiods of use.

The soft vulcanizable rubber composition used as the backing material inthe present plate can be stored for relatively long periods of timewithout appreciable change in its vulcanizing characteristics, so thatthe printer will have no difficulty about fabricating a printing platefrom it, even if the material has been on hand for some time. This istrue also of the composition used as the facing material, since itremains in the desired heat-curable condition'throughout relativelyprolonged times in shipment or storage. There is therefore no diflicultyabout the printing plate material deteriorating during the time elapsedbetween manufacture of the material and fabrication of the plate. v

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

A printing plate laminate comprising a composite flexible sheetconstituted of a relatively thick resilient backing layer ofsoft-vulcanizable nitrile rubber directly heatlaminated on one surfaceto a contacting surface of' a relatively thinner facing layer of a hardbut flexible composition comprising a heat-curable blendof parts ofnitrile rubber with from 25 to parts of a cashew nut shell oil modifiednovolac phenol-formaldehyde resin, the said nitrile rubber in each saidlayer being a copolymer of butadiene and acrylonitrile containing from10% to 50% of acrylonitrile and the presence of said nitrile rub her ineach said layer serving to enhance the adhesion between the layers, thesaid laminatedlayers being characterized by the ability to retainwithout appreciable change their original'vulcanizing and curingcharacterable, when heated to softening and curing temon deiicatesurfaces Without damage thereto and flexible enough to conform Withoutdifiiculty to the curvature of 10 a printing plate cylinder.

References Cited in the file of this patent UNITED STATES PATENTSHarbison et a1. Sept. 10, Swan et a1. June 21, Freedlander July 14,Gartrell Mar. 18, Juve et a1 Jan. 27, Groten et a1 Jan. 18,

